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From Hadrian Zbarcea <hzbar...@gmail.com>
Subject Re: Components setting data on OUT
Date Mon, 26 Jan 2009 18:37:24 GMT
I don't disagree, I was just suggesting that they should then travel  
as properties.  Whatever we name them, and whatever mechanism we  
decide to use, as pointed out before, we need to distinguish between  
headers that are endpoint/protocol specific and have no semantics  
outside the endpoint and headers (which we called properties and  
didn't use consistently) that must be carried over the lifetime of the  
Exchange.

Hadrian


On Jan 26, 2009, at 1:07 PM, William Tam wrote:

> On Mon, Jan 26, 2009 at 10:35 AM, Hadrian Zbarcea  
> <hzbarcea@gmail.com> wrote:
>> Hi,
>>
>> This headers business is a bit of a tricky one.  I hit it last year  
>> in the
>> context of security.
>>
>> I agree with the view that headers should only exist in the context  
>> of an
>> endpoint.  I think outside of that there is no guarantee that the  
>> semantics
>> of a header is preserved.  I am not sure if headers should be  
>> propagated
>> from one endpoint to another at all.
>
> There are certainly use cases that protocol headers DO need to be
> propagated between endpoints.  If users want to integrate with some
> management and/or security tools like Actional, users are required to
> include custom headers in protocol headers.  These custom headers
> travel with messages to allow trust zone enforcement and message
> correlation.  They need to be preserved and propagated across hops
> which are potentially over different transport protocols.
>
>> Properties should be used instead.
>> Coming back to security, if http is used for instance there are  
>> several ways
>> of handling that.  If basic auth is used for instance one gets a  
>> user/pass,
>> but that may need to be translated to something else at endpoint  
>> boundaries.
>> I don't think that the "Authorization" header should exist outside  
>> the http
>> endpoint for instance.
>>
>> Yes, we do propagate properties today, no issue there.  But then some
>> policies need to be defined per endpoint to deal with known
>> headers/properties, and camel specific properties should be defined  
>> to deal
>> with know headers.  Even better, endpoints should set protocol  
>> specific
>> headers that are known as required to propagate (such as the auth  
>> stuff) as
>> properties from start.
>>
>> My $0.02
>> Hadrian
>>
>>
>> On Jan 26, 2009, at 9:44 AM, Claus Ibsen wrote:
>>
>>> On Mon, Jan 26, 2009 at 3:37 PM, Roman Kalukiewicz
>>> <roman.kalukiewicz@gmail.com> wrote:
>>>>
>>>> Why don't we talk about exchange properties here? My feeling here  
>>>> is
>>>> that properties should be used as user-headers, while headers are
>>>> always protocol headers. In fact it works this way right now: If I
>>>> want to keep some value through the whole flow I put it into
>>>> properties.
>>>>
>>>> By current convention if I put something on a header it is sent as
>>>> protocol-specific header (JMS property, HTTP header), and out  
>>>> headers
>>>> are filled also with protocol headers (JSM properties of out  
>>>> emssage,
>>>> HTTP response headers). In this case headers shouldn't be  
>>>> propagated,
>>>> as there is no way to distinguish things propagated, from things
>>>> retrieved. And out headers ARE different than in headers.
>>>>
>>>> It is a matter of naming, but currently headers are (what you call)
>>>> protocol/system headers, while properties are user-headers (work as
>>>> variables). Do we really need to extend it further? If someone mix
>>>> those two concepts then it is problem of documentation, but not  
>>>> lack
>>>> of functionality. I would just extend DSL a little to be able to
>>>> retrieve a property (instead using header()).
>>>>
>>>> What do you think, guys? Maybe we should clearly communicate what
>>>> things are for and what are the consequences of using one or  
>>>> another.
>>>>
>>>> Roman
>>>>
>>>> PS. Pipeline should propagate all headers of course, but I  
>>>> believe an
>>>> endpoint is a place where we shouldn't guarantee that headers  
>>>> will be
>>>> propagated by stating it clearly.
>>>
>>> Properties have just lived in the dark and end users does not really
>>> know they exists. We have some builder methods to set/get  
>>> properties.
>>> I guess we need to document and maybe make sure the Spring DSL also
>>> has support for accessing properties as well.
>>>
>>> To my knowledge properties is always preserved so I doubt we have an
>>> issue there.
>>>
>>> So users should just start learn using properties as well :)
>>> However then we have the ProducerTemplate that has one liners for
>>> sending an Exchange. We dont have a sendBodyAndProperties method.  
>>> But
>>> yet again it has too many methods already. They can just use
>>> send("xxx", Exchange) and have exchange populated with the  
>>> properties
>>> of choice.
>>>
>>>
>>>
>>>
>>>>
>>>> 2009/1/26 Claus Ibsen <claus.ibsen@gmail.com>:
>>>>>
>>>>> On Sat, Jan 24, 2009 at 9:08 PM, William Tam  
>>>>> <email.wtam@gmail.com>
>>>>> wrote:
>>>>>>>
>>>>>>> What we have stored in Headers today in Camel is both:
>>>>>>> - user headers
>>>>>>> - and system headers (added by Camel itself).
>>>>>>>
>>>>>>> I am starting to be more and more convinced that we should  
>>>>>>> separate
>>>>>>> the two.
>>>>>>> So any headers that a users has enforced to be set should be
 
>>>>>>> kept in
>>>>>>> one Map and the others that the components set internally  
>>>>>>> (such as SQL
>>>>>>> number of rows returned, or whatnot we have, there are many)
in
>>>>>>> another Map.
>>>>>>>
>>>>>>
>>>>>> It means that a component would have to look for header in more 

>>>>>> than
>>>>>> one place.   Besides, the distinction of user vs system header  
>>>>>> is not
>>>>>> always clear.  For example, the operation name header for cxf  
>>>>>> endpoint
>>>>>> can be set by user but it is also created by cxf component.   I 

>>>>>> am
>>>>>> sure there are many more examples.  There is another header  
>>>>>> category:
>>>>>> protocol headers.  A protocol header is not really a user or  
>>>>>> system
>>>>>> header.  Protocol headers are header propagated from protocol  
>>>>>> like
>>>>>> HTTP, which we do want to preserve in message header.
>>>>>>
>>>>>>> The user headers is always preserved and copied along in the
 
>>>>>>> routing.
>>>>>>> User can always clear/remove unwanted headers.
>>>>>>> The system headers should be short lived as they are not really
>>>>>>> useable. So they are "alive" in the next step (process) in the
 
>>>>>>> route,
>>>>>>> and when the pipeline invokes next route thereafter these  
>>>>>>> information
>>>>>>> is cleared.
>>>>>>>
>>>>>>> Separating these will also make the routing/tracing a bit  
>>>>>>> easier as
>>>>>>> Users can recognize their own headers instead its mixed with
 
>>>>>>> all the
>>>>>>> noise the Camel components add.
>>>>>>>
>>>>>>
>>>>>> I wonder we can leverage/extend the HeaderFilterStrategy  
>>>>>> mechanism.
>>>>>> Currently, it is only used for filtering unwanted headers (in  
>>>>>> both
>>>>>> request and response direction) when we propagate headers between
>>>>>> Camel and external messages (like HTTP).   HeaderFilterStrategy 

>>>>>> is (or
>>>>>> will be) associated with an endpoint.  We could make
>>>>>> HeaderFilterStrategy available to the exchange object.  So,  
>>>>>> when an
>>>>>> endpoint creates an exchange, the exchange gets a header filter
>>>>>> strategy.  Then, pipeline can do something like this to filter
>>>>>> unwanted header: message.filterHeaders().   The header filter  
>>>>>> strategy
>>>>>> is highly customizable for each endpoint (can have a component  
>>>>>> wide
>>>>>> default) and it can be looked up from registry.
>>>>>>
>>>>> Good pointers William.
>>>>>
>>>>> Yeah we can revist it after you have moved the header filters to  
>>>>> the
>>>>> endpoint.
>>>>>
>>>>> Then we can check up upon how to leverage it as you suggest.
>>>>>
>>>>>
>>>>> --
>>>>> Claus Ibsen
>>>>> Apache Camel Committer
>>>>>
>>>>> Open Source Integration: http://fusesource.com
>>>>> Blog: http://davsclaus.blogspot.com/
>>>>>
>>>>
>>>
>>>
>>>
>>> --
>>> Claus Ibsen
>>> Apache Camel Committer
>>>
>>> Open Source Integration: http://fusesource.com
>>> Blog: http://davsclaus.blogspot.com/
>>
>>


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